LABREADOR: A zero-footprint, client-side web application for automated quality control and nonlinear regression in...

Quantitative analysis of microplate bioassays, such as ELISA, requires robust nonlinear regression tools. These are typically available either as expensive commercial software or as simple web-based alternatives with insufficient analytical capabilities. In this work, we present Labreador-a freely available web platform built on a client-side architecture that eliminates the need to transfer data to external servers. The system integrates automated selection from five regression models (including 4PL and 5PL) with the Levenberg-Marquardt optimization algorithm, weighted regression for heteroscedasticity correction, interactive outlier management, and a three-level quality control system with automatic blocking of interpolation when the calibration curve quality is insufficient (R² < 0.95). The platform's accuracy was verified on a synthetic reference dataset. Following the application of 1/Y² weighted regression and interactive outlier management, the algorithm recovered an excellent fit (R² ≥ 0.98) and the true EC₅₀ reference value of 150.0 fell within the recovered 95% confidence interval, confirming the statistical validity of the parameter estimate in the presence of 10% CV biological noise. Labreador provides robust computational accuracy sufficient for rigorous laboratory practice in a free, privacy-oriented environment accessible without any technical barriers.